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[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

I finally had some time to play around with this locally (not on AWS, so
things still might differ as there could be a dependency on the version
of the Xen hyperviror as well). The default setup I used initially
failed for memory issues. But then I used full server installations in a
HVM guest (which brings many more modules). So tweaking the modules to
include by setting

/etc/initramfs-tools/initramfs.conf:
MODULES=dep

and

/etc/default/grub.d/kexec-tools.cfg:
crashkernel=256M

may or my not be required for EC2. The main problem seemed to be related
to unplugging the emulated devices (in favour of the pv drivers). The
only variant that seemed to partially work for me was to use
"xen_emul_unplug=never" for the normal boot. Of course this is not
really ideal as this impacts normal usage performance. This also only
worked as much as creating a dump but it took a bit of time since the
network interface would not come up.

A RH bug suggests a slight variation which supposedly avoids using the
emulated drivers. But either I mis-read the instructions or it just does
not work in our environment. At least those attempts just hung like
before.


[1] https://bugzilla.redhat.com/show_bug.cgi?id=815785

** Bug watch added: Red Hat Bugzilla #815785
   https://bugzilla.redhat.com/show_bug.cgi?id=815785

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https://bugs.launchpad.net/bugs/1421391

Title:
  can't kdump in trusty ec2 instance

Status in linux package in Ubuntu:
  Incomplete

Bug description:

  [Impact]

  I can't get a crash dump in an ec2 trusty instance. When it kexecs, I
  see the following backtrace:

  [    0.813826] ------------[ cut here ]------------
  [    0.817517] WARNING: CPU: 0 PID: 1 at /build/buildd/linux-3.13.0/arch/x86/mm/ioremap.c:102 __ioremap_caller+0x374/0x380()
  [    0.823494] Modules linked in:
  [    0.825807] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-44-generic #73-Ubuntu
  [    0.829917] Hardware name: Xen HVM domU, BIOS 4.2.amazon 12/03/2014
  [    0.833266]  0000000000000009 ffff8800362f1c18 ffffffff81720d86 0000000000000000
  [    0.838861]  ffff8800362f1c50 ffffffff810677cd ffffea0000ff0640 000000000003fc19
  [    0.844463]  000000003fc19000 000000000003fc19 0000000000001000 ffff8800362f1c60
  [    0.850005] Call Trace:
  [    0.851708]  [<ffffffff81720d86>] dump_stack+0x45/0x56
  [    0.854563]  [<ffffffff810677cd>] warn_slowpath_common+0x7d/0xa0
  [    0.857735]  [<ffffffff810678aa>] warn_slowpath_null+0x1a/0x20
  [    0.860855]  [<ffffffff81056ba4>] __ioremap_caller+0x374/0x380
  [    0.864047]  [<ffffffff8104b528>] ? copy_oldmem_page+0x48/0xc0
  [    0.867193]  [<ffffffff81056be4>] ioremap_cache+0x14/0x20
  [    0.870123]  [<ffffffff8104b528>] copy_oldmem_page+0x48/0xc0
  [    0.873223]  [<ffffffff81231fd4>] read_from_oldmem.part.0+0xa4/0xe0
  [    0.876534]  [<ffffffff8123222b>] elfcorehdr_read_notes+0x1b/0x20
  [    0.879797]  [<ffffffff81d66809>] merge_note_headers_elf64.constprop.7+0x71/0x24a
  [    0.883949]  [<ffffffff81d67188>] ? vmcore_init.part.4+0x55d/0x55d
  [    0.887380]  [<ffffffff81d66dbd>] vmcore_init.part.4+0x192/0x55d
  [    0.890670]  [<ffffffff81d67188>] ? vmcore_init.part.4+0x55d/0x55d
  [    0.894075]  [<ffffffff81d671b9>] vmcore_init+0x31/0x33
  [    0.897022]  [<ffffffff8100214a>] do_one_initcall+0xfa/0x1b0
  [    0.900121]  [<ffffffff81089555>] ? parse_args+0x225/0x3f0
  [    0.903231]  [<ffffffff81d360f6>] kernel_init_freeable+0x17b/0x200
  [    0.906683]  [<ffffffff81d358e5>] ? do_early_param+0x88/0x88
  [    0.909814]  [<ffffffff8170f250>] ? rest_init+0x80/0x80
  [    0.912777]  [<ffffffff8170f25e>] kernel_init+0xe/0x130
  [    0.915648]  [<ffffffff817317bc>] ret_from_fork+0x7c/0xb0
  [    0.918684]  [<ffffffff8170f250>] ? rest_init+0x80/0x80
  [    0.921565] ---[ end trace 8b6e218b41648bbd ]---

  [ Test Case ]

  boot ec2 trusty instance
  sudo apt-get install linux-crashdump
  sudo sed -i 's/USE_KDUMP=0/USE_KDUMP=1/' /etc/default/kdump-tools
  sudo reboot
  sudo kdump-config show
  echo c | sudo tee /proc/sysrq-trigger

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